Most languages (including English) distinguish between relative clauses, embedded declarative clauses, and embedded interrogative clauses in various syntactic ways (e.g. complementizers, gaps, wh-words, extraction). The syntactic behavior matches the semantic one, since all these embedded clauses differ in their meaning as well. In this talk, we present a language that exhibits a very different pattern. In Adyghe, a North-West Caucasian language spoken in southern Russia and some parts of Turkey, the very same “mystery clause” is used to convey the various meanings that relative clauses, embedded declaratives, and embedded interrogatives convey in other languages. We show that (i) Adyghe’s “mystery clause” is a headless relative clause, and that (ii) the syntax-semantics mapping in Adyghe can be accounted for by means of tools that have already been independently argued for in the grammar (set formation, concealed questions, polarity operators, etc.). More generally, Adyghe and its extensive use relative clauses to convey various meanings show that the syntax-semantics interface across languages is more varied that it is usually assumed, but it can still be handled without enriching the conceptual apparatus of the grammar.